1. Field of the Invention
The field of art to which this invention pertains is aromatic polyamide fibers and, more particularly, it is directed to processes for making such fibers.
Specifically, such invention is a process for dyeing a fiber structure of poly(meta-phenylene isophthalamide) fibers with a water-soluble dye by heating the amorphous, water-swollen fibers, as spun and prior to drying, with steam at a temperature from about 110.degree. C. to 140.degree. C., and preferably at about 120.degree. C., for a time sufficient to diffuse substantially all of the dye into the minute pores in the fibers, throughout the fiber structure.
An organic water-insoluble material, such as an ultraviolet light screener, may also be mixed with the water-soluble dye and padded onto the water-swollen fibers prior to heating. While the dye is effectively diffused into the fiber structure at temperatures between 110.degree. C. and 140.degree. C., such structure must also be heated with steam at a sublimation temperature below the glass transition temperature of the fibers in order to sublime the screener into the pores of the fibers. The fibers are then, preferably, further heated with steam at about 165.degree. C. for a time sufficient to collapse the pores in the fibers and lock the dye therein. At this temperature the fibers also will crystallize and the fiber structure is thereby stabilized against progressive laundry shrinkage.
Various water-insoluble materials, including disperse dyes, may be driven into the fibers in this manner (e.g., by contacting the water-swollen, never-dried fibers with a dispersion containing the dye and heating with steam to 165.degree. C.). Preferably this sublimation step follows the diffusion step previously described.
2. Description of the Related Art
Aromatic polyamide fibers are well known to the art. They have high tensile strength, are flame and heat resistant, possess good flex life, and have very high melting points, etc. which make them particularly suited to be formed into fabrics usable as protective clothing, and for many other uses.
It further is known that while aromatic polyamide fibers possess many desired properties as manufactured they also require, for given uses, that various steps be taken to improve a property or properties of the fibers to meet a specific end use. As an example, various additives such as dyes, ultraviolet light screeners, flame retardants, antistatic agents or water repellents, may be incorporated into the fibers during basic manufacture or in subsequent processing steps to improve their performance levels.
This invention is specifically directed to aromatic polyamide fibers of a poly(meta-phenylene isophthalamide) polymer, hereinafter referred to as "MPD-I fibers". Such fibers, which are described in greater detail in U.S. Pat. No. 3,287,324 to Sweeny, for example, possess many useful properties. It is well known to the art, however, that these fibers are very difficult to dye.
Various techniques have evolved to solve this dyeing problem. A typical solution, well known to the art and widely practiced, dyes the fibers in an aqueous bath in the presence of a carrier, such as acetophenone. While this is an acceptable method for dyeing such fibers, the carrier is expensive and must be disposed of.
Another solution is shown in British Pat. No. 1,438,067 to Moulds and Vance which teaches imbibing a polyoxyethylene laurate impregnant into never-dried MPD-I fibers by passing such fibers through an aqueous bath, prior to dyeing. The impregnant serves as a "structure prop" which prevents collapse of the water-swollen fibers on drying. The dried impregnated fibers may subsequently readily be tinted in an aqueous dye bath while corresponding fibers dried without the impregnant may be tinted only under much more vigorous conditions, including necessarily the use of dye carriers, such as acetophenone, as mentioned hereinabove.
This invention solves these and other problems found in the prior art by surprisingly finding that by heating as-spun, never-dried, water-swollen MPD-I fibers with steam, heated within certain temperature ranges, it is possible effectively to dye the fibers. Specifically, it has been found that such fibers may be dyed, using a water-soluble dye, by heating the fibers with steam heated at a temperature from about 110.degree. C. to 140.degree. C. for a time sufficient to diffuse the dye into the pores of the fibers.
It further has been found that after this diffusion step has taken place that such fibers may be subsequently heated, again with steam, at a temperature of about 165.degree. C. to collapse the fibers and lock the dye in place. This latter step will also, it has been found, crystallize the fibers and stabilize them against progressive laundry shrinkage.
In addition, various organic water-insoluble materials, such as ultraviolet light screeners, may be mixed with the water-soluble dye and driven, by a sublimation heating step, into the fiber pores. Again, heating is accomplished with steam, while the pores remain open and sublimation temperatures from about 110.degree. C. to 150.degree. C. are required to sublime the water-insoluble materials into the open pores.
Accordingly, this invention provides improved processes for making aromatic polyamide fibers, using steam in all cases as a key step, to dye a water-swollen fiber structure of poly(meta-phenylene isophthalamide) fibers with a water-soluble dye, before they are dried, or to add an organic water-insoluble material to the fibers, either mixed with the dye or alone, and to lock the dye and/or other impregnant into the pores of the fibers. This is accomplished by using critical steam temperatures (e.g., 110.degree. C. to 140.degree. C.) to diffuse the dye into the fiber pores and up to 165.degree. C. to sublime the water-insoluble material into such pores. At this latter temperature the dye is also locked into the fibers, while stabilizing such fibers against progressive laundry shrinkage. These processes give to the fiber-making and dyeing arts a highly sought capability, and a practical means of solving a number of problems long challenging such arts.